Variable pitch propeller



Dec. '11, 1951 w. L. GREENE 2,578,350

- VARIABLE PITCH PROPELLER Filed June 1, 1944 I 3 Sheets-Sheet l 7 v i 5 r 5 1 Dec. 11, 1951 W. L. GREEN E VARIABLE PITCH PROPELLER Filed June 1, 1944 WI V V J Z0 52 3 Sheets-Sheet 2 E6 VV/LL/AM L. GREENE Dec. 11, 1951 I GREENE 2,578,350

' VARIABLE PITCH PROPELLER Filed June 1, 1944 a Sheets-Sheet 5 DECREASE A PITCH PITCH OECREAS/IVG MOI 5M6? ARRES Tffl 8) INCREASL'D SPEED OF R0714 T/O/V VALVE POSITION O I N GREASE /rcH INCREASING' MOVEMENT AIPRtSTEO Ar r/ms PO/IVT BY awe/Ive COMPRESSION O 50 I00 l 50 Z00 AIRSPEED ZIOOREH ZOO REM. 1800 REM. ZIOO R.P.M.

MAL/AM L. GREf/VE m WJZAA U721" WW,

Patented Dec. 11, 1951 UNITED STATES PATENT-OFFICE 2,578,350 VARIABLE PITCH \PROPELLER William L. Greene, Washington, D, 0., asslgnor to Engineering and Research Corporation, Riverdale, Md., a corporation of Maryland Application J unel, 1944, Serial No. 5 38 ,248 B'Clailn's. "(01. 170-46021) Phis inventionrelates to variable pitch propellers and, more particularly, to those of such propellers which automatically operate to main- .tain a constant, predetermined engine speed.

It is aprincipal object of the invention to provide; in a deviceof thetype described, meanscontainedin the propeller assembly and not requiring-manual or other control by the pilot, which will cause the propeller to maintain any of one or more predetermined engine speeds. Thus, for certain conditions, such as take-off, it may be :desirable to maintain the engine speed at a certain constant value, or within a predetermined range, while for other conditions, such as level flight at high speed, it may be desirable to main- .tainthe engine speed at another constant value .or within a range different from the value or range desired for the other condition. This governing ofthe propeller and engine speed at these values or ranges of speedis provided by the present invention and permits operation at optimum conditions at the speed levels at which the conditions of governing occur.

It is another principal object of the invention to provide pitch-varying means for a variable .of-operating fluid to ,the fluid motor, means which .are controlled by the speed .of rotation 0f the propeller for .operating the valve means to .so regulate the flow of fluid to the motor as to cause the pitch of the propeller to be adjusted in .accordancewith the .speed of rotation of the propeller.

Another object of the invention is .to provide means in La fluid-pressure operated pitch-varying system ior'limiting the increase .or decrease -;of -pitch to ,predetermine values.

Other objectsandJfeatures, of novelty of the "invention will be .madeapparent'by the following description and the annexed drawings thedisclosure of whichfit vwillbe understood, is only illustrativeof the'inventionan'd imposes nolimi- .gtation Ithereon -not imposed by the appended claims.

ii 'Referring- -to therdrawings, which tfiimila $1 ,eference characters refer .to .like parts,

'Fig. .llis a.sectiona1 view .through a propeller,

. :hub and shaft. assembly including :pitch chang- 2 ing means and a control therefor, all according to the invention;

Fig. 2 is .a view on a reduced scale taken on line .2-.2 .of Fig. .1;

Fig. 3 is a viewof parts shown in Fig. 1 and illustrating the valve position, at high speed, to increase the pitch;

Fig. 4 is a view similar .to Fig. 3 illustrating the valve in blanking position after the control means have assumed a state of equilibrium;

Fig-5 is a viewof parts shown in Fig. 1 illustrating the operation of the means which permit constant speed maintenance at a level difierent .from thateflected during operation as illustrated .in Fig.3;

Fig. sis agraphic illustration of themovement -rof the valve in arriving at a position in which constant propeller speed is maintained, and

Ei 7 is apartlv dia r mm view s owi an embodiment of the invention having means .for efiec'ting constant Speed maintenance at a plurality .of levels.

Inithe .drawings there is disclosed a preferred .form oithe invention which comprisesthe drive shaft 2 to the endof which is attached a cylindrica'lhub 4 in .the opposite open endsof which are arranged two plates,6,j.3, which are held from inward movement by flanges l0 extending radially inwardly from the wall of the hub 4, and which are heldfrom outward movement byrings {2 which are ,threadedly attached within the oppositeopen ends of the hub jand are separated from theplates 6, ,8 by ball bearings I4 whereby the; plates are freely rotatable. A propeller. blade [6 is attached ,to each of the plates 6, 8 by threaded bolts [8 and extends therefrom radially of the .shaft ,2. It will .be obvious that rotationlof the shaft .2 .willdcause rotation of the blade system .in :the usualmanner of a propeller, and that each blade and its attached plate Ger 8 maybe rotated about .theaxis thereof .in .order to eflect pitch variation.

vMeans are provided .by .the invention .for changing the .pitchoflthe blades .6, .B andsuch means comprise-a movablecylinderzfl which is disposed .within -theehubui with its axis-at right anglesto 1 the-.axis-of .thehub-andof the blades and parallel .to :theaxis {Hf the -:drive- -shaft '2. The cylinder surrounds a fixed disc or. piston 22 which .is attached :atzits centeratoeartube 2.4 which extends forwardlydromtheicenter-of'a plate 26 WhiOhilS attached to-the hub Aandwhich closes the :forward-end-of-;the'hollow crankshaft shaft 2,*forming therein-a chambera'ZB which is supplied-with thesnormal rengine lubricant which is already under pressure .ith oush a e i P01171530 which; extends through ;the wall of the crankshartand {through .2. bearing 32 therefor. 1 The cylinderilll isprovided-exteriorly with oppositely- -eextending ears. whichare-respectively connected, by pins 35 to the adjacent plates 6, 8 eccentrically thereof. The cylinder is slidably longitudinally of the tube 24 and wi h respect to the fixed disc or piston 22 and it will be apparent that if fluid under pressure is supplied to one or the other side of the piston the cylinder will be moved, with respect to the piston, thereby causing the plates 5, 8 and the blades I which are attached thereto to be moved. about the axis of the respective blades to vary the pitch thereof.

Means are provided by the invention for introducing fluid to one or the other side of the piston 22 within the cylinder 20 and exhausting it from the other side in order to cause a corresponding movement of the cylinder. Such means comprise, broadly, a system of ports connecting the various parts of the system to a valve chamber, and valve means within the chamber for distributing the pressure fluid. The valve chamber is formed by a passage 55 which extends longitudinally and centrally of the tube 24. The valve means comprises a stem 56 which is slidably mounted within the passa e 55 and has spaced, reduced diameter parts 58, 60, 62 which are separated by spaced enlarged parts 64, 66, 68 which are of the same diameter as the inside of the passage 55 and as the main part of the valve stem, thus providing three separated, annular chambers I0, 12, 14 between the three reduced-diameter parts of the valve stem and the inner wall of passage 54. The rearward part of the axial passage 55 through tube 24 communicates with the exhaust passage 40.

The port system comprises a high pressure inlet port 80 which extends longitudinally through the wall of tube 24 exteriorly of passa e 55 and communicates as its one end with the high pressure reservoir 28 and at its other end with the interior of the reduced-diameter passage 55 through the central port 82 of three ports, which central port is disposed at about the middle of the piston 22. The forward port 84 of the three ports connects the interior of the valve chamber 55 to the interior of cylinder 20 at the forward side of piston v22, while the rearward port 86 of the three ports connects the valve chamber 54 with the interior of the cylinder at the rearward side of the piston. The three ports 82, 84, 86 are preferably aligned longitudinally of the tube 24. In another part of tube 24 there is formed a longitudinally-extending passage 90 which communicates at its rear end with the exhaust passage 40 and at its forward end with the valve chamber 55 through two spaced ports 92, 94 which are respectively positioned just outwardly of the two ports 84, 86.

The spacing of the parts of the port and valve systems and the range of movement of the valve are such that when the valve stem 56 is in such position that the central or high-pressure port 82 is communicated through annular chamber I0 or 12 with cylinder inlet passage 84 or 86, the other cylinder inlet passage will be connected to exhaust port 92 or 94 through one of the annular chambers formed by the reduced-diameter parts of the valve stem. Thus, when the valve stem is in' the pos i-' tion shown in Fig. 1 high pressure fluid flows from reservoir 28, through passage 80, port 82, annular chamber I2 and port 85 to the cylinder 20 on the right-hand or rearward side of piston 22. At the same time the left-hand or forward side of the cylinder will be connected to exhaust passage '40 through port 84, annular chamber I0, port 92, 'and passage 90.

The cylinder will therefore be moved to the right (or rearwardly) and in the preferred mode of operation of the invention such 4 movement of the cylinder will cause reduction of pitch of the blades.

If the valve stem is moved to the right from the position shown in Fig. 1 to that shown in Fig.

.3 the high-pressure supply port 82 communicates with the cylinder inlet port 84, but is blanked off from cylinder inlet port 85. At the same time, outlet port 92 is blanked by the enlarged part of valve stem 55, and outlet port 94 is communicated to cylinder port 86 through annular chamber I0. Thus, fluid under pressure flows to the cylinder at the left-hand or forward side of the piston and is exhausted from the right-hand or rearward side, thereby causing the cylinder to move forwardly or to the left as viewed in Fig. 6 and, in the preferred embodiment of the invention, causing pitch-increasing movement of the propeller blades.

In the valve position shown in Fig. 4 the enlarged part 64 of the valve stem blanks off the high pressure inlet port 82, while the valve rod 56 and the enlarged part 66 blank off the outlet ports 92 and 94. In this condition flow of fiuid to or from the cylinder chambers is stopped and the cylinder is maintained in its position at the time the valve reached the blanking position. This position is assumed by the valve when the valve control means, whch are described hereinafter, reach a condition of equilibrium such as is shown in Fig. 4.

Means are provided by the invention for operating the valve means in accordance with the speed of rotation of the propeller and such means comprise centrifugally-operated devices which move the valve means in one direction as the speed of rotation increases, and spring means which constantly urge the valve in the opposite direction. In the disclosed embodiment a cylindrical housing I00 is threadedly connected to the forward wall of the hub 4 and on spaced parts of the interior wall thereof are pivotally mounted one or more centrifugally-operated devices I02. Each of these devices comprises two integrally united angularlyrelated arms I04, I06 which extend in different directions from the pivotal support of the centrifugal device of which they form a part. Each arm I04 is so positioned that it engages the forward face of a collar or abutment member I08 which is screw-threaded to the forward end of the valve rod 56. Each arm I06 is so positioned that it may freely move under the action of centrifugal force, thereby moving arms I04 and causing the valve rod to be moved in accordance with changes in centrifugal force and therefore in response to changes in the speed of rotation of the propeller system. A compression spring I I0 bears at its one end on the rearward part of the collar I08 and at its other end on the forward end of a two-part device I I2 which is threadedly connected to the forward end of the tube 24, and the spring therefore constantly urges the collar I08 and the valve rod in a forward direction, resisting the efiort of the devices I02 under the action of centrifugal force to move the valve rod to the rear.

The parts are so constructed and arranged that when the speed of rotation of the propeller system reaches a pre-determined level the centrifugally-operated means will move the valve rod in pitch-increasing direction, 1. e. to the right as shown in the drawings, against the force of spring IIil, while the spring will maintain the valve parts in their left-hand, or pitch-decreasing position, as shown in Fig. 1 of the drawings so long as the centrifugal effort of the'arms I06 is less than the force of the spring means.

Means are provided by the invention for adsegtragsso justably limiting thef'pitch-decreasing movement mi the parts.

Such means "comprise a 1 tubular member I20 connected concentrically to the forlward end of the'cylinder'2'0 and:extending'forwa-rd1y therefrom and" a -second' tubular member I 22- extending' 'rearwardly: from thehub-carried tubular "member I til and surrounding-and being concentric with the member I213. "The relatively fixed member l22 has an inturned flange I24 on its rearward end which is in the path of and engageable by'a radical'flange I 26 which extends outwardly from the wall of member I20. The member I22 is preferablyscrew-threaded at its forward end to the member IIlli'in order that the position of the abutment or'stop' I24 'may'be -cha'n'ged. It will 'be-seen that pitchdecreasing operation.

The operation of the described parts I as a speed-governing means will now be described, reference being made to "the curve of Fig. 6 as well as to the other figures. When the aircraft is on the ground and thep'ropeller is idling the centrifugal force exerted by arms I06 isless than the force of the opposing spring means Hi! and [the .spring means therefore hold the valve means in the position shown in Fig.1, in which the cylinder 20 is moved to its most extended position in :a pitch-decreasing" direction, being held from further movement by the 'stop means I24,

I26. "The condition of the system'at this time :--is represented by point 'A on thecurve of Fig. 6, atwhich the air-speed is'zero and'thepitch aIigIe is a minimum. As the aircraft moves forward to takeoif, the centrifugal force on devices I02 -does not increase sufficiently to overcome the action of spring I I and the valvepartsareheld :in the .minimum-pitch -:position during this i 'period. .Asthe aircraft approaclies level' fiight "conditions the power theretofore utilized in take- :ofi andc'limbing is translated into increasedprojpeller speed and the actionof 'centrifugalforce on devices 12 begins to overcome the effortpf :the spring EH3, causingthe "valvexmeans to so move that eventually, as shown'atlpointB, the pitch-changing means are caused to ximove in ;:;pitch-;increasing directiomriue. thei'cylirider 20 nmovesto. theleft as shown" in Ithef'drawings. The

.zpositions of :the partsz-at @the beginning ofth-is 1i'rrmvemerit are illustrated in Fig-3, when-ith'e oforce or .the compressed spring becomes-greater athan the centrifugal 'forcea a'ctingon devices 'I'02,'*the I the valve parts =will he moved toithe-leftfcausing thecylinder"2!! to m'ove to the' right'to decrease "the ,pitchpofthe blades. Buch'decre'ased'ipitch willcausethe speed of rotation torbe increased, "in accordance with well-=known lawsjand the dome of :the :centri-fugaladevices I92 iwill again -overcome :that of: spring I HI, tmoving zithefvalve parts to spitch-increasing position, :from which :ithepartswill be'imoved to pitch -in'creasin-"g? posizztiongand soton. Each successive'ipitchsincreas- H :fin'g or .pitch-decreasing ;.movement i will ibe 'of :r shorter duration thanthe preceding'onei whei-eby itheesystem will finally reach a stable condition was .shownat: point Dkin' Fig." w-hich will :belia (pitch condition, i. e. a position-of cylinderrlll,

which will beaoptimuni-for the speed-of rotation :of the spropeller'system" and therefore for-the eexistihgair-speed. Only'averysho'rt period :of

-=-;time; for 'example a few seconds, will be required 'shut 01f, thereby ho'ldingthe propeller from further pitch-changingmovement so long as the ex- :iisting'conditioniof flight remain unchanged. The centrifugal devices I62 and spring III! are now in "a state of equilibrium.

The'described system will operate asv a speed governor for the propellersystem as a 'pre-de- 1 termined speed, for example 2000 R. P."M.,which is selectable by proper'design'and proportioning "of .the spring III! and the centrifugal-devices I02. After the propeller system reaches a stable condition at this speed, any variation from such 'rangewill cause one or the other of the forces in equilibrium, i. e. the spring and the centrifugal devices, to overcome the other, thereby increasing or decreasing the pitch and decreasing or 'increasing the speed of rotation of the system'to the lore-determined range. "For example, assume that'the aircraft is in'level flight and the rotary speed of the propeller is at the" prescribed level. If the aircraft now beings to climb, the rotary speed will decrease because the decrease in forward s'peed'of'the' aircraft causes a heavier load "on the blades, the centrifugal force acting'on devices Q32 will decrease, and the spring IIB will move the valve' parts to the left'from their'position as shown in Fig. 3, causing the pitch tobe decreased and thereby increasing the speed. "The *speed will not increase above the prescribed range as the centrifugally-operated devices will move the valve parts to pitch-increasing (speed decreasing) condition before the upper speed limit is reached.

Means are provided by the invention for causing the pitch-controlling system to govern'the speed of rotation of the propeller systemat two 'or'more speeds. Thesystem heretofore described will operate to maintain a constant speed of rotation at one level, for example 2000 R. P. 'while that to be described'hereinafter will maintain constant speed at another level, for example at 2500 R. P. M. The means for shooting this comprise, generally, means for changing the force exerted by the compression spring Illi'but might, with equal effect, comprise means for changing the force exerted by the'oentrifugal devices I52 at'a given speed. In the disclosed *emb'odimento'f the'invention such means comprise the two-part abutment H2 against which the rear end of spring I II! bears, and which comprises'arear part let! having a cylindrical part I52 interiorly 's'crew-threa'dedto the'exterior" of tube 24 and a radially extending flange I 54. The abutment ll2'als'o includes a forward member I55 having 'acylindrical part I58'which slidably surroundsthecylindrical part I52 of the member 5ll,=and also hasa radially-extending flange I59 against which the rear end of spring Iii! bears 'and which is constructed and'adapted to honorma11y pressedby the spring into face-to-face 'engagement'with th'e flange I54. The inner suri faces of the outer peripheral parts" of the flanges I54, I58 are inclined toward each other to form a stright-sided ball race receiving the balls I60. The abutment H2 is within the cylindrical extension I2Il on the forward end of cylinder 20 and the flanges I54, I58 are so constructed and proportioned that the balls I60, which are between such flanges are held by the cylindrical extension I2Il in an inner position, as shown in Figs. 1 and 3, in which the flanges are held apart, the flange I58 being moved from the flange I54 against the force of spring III].

The inner wall of the cylindrical extension I29 has an annular groove I80 of substantial axial extent formed therein. This groove is spaced from the forward end of the member I29 and so long as the balls I60 engage the surface between such end and the groove they Will hold the flanges I54, I58 apart in the described manner. Suflicient leftward, or pitch-increasing, movement of the cylinder 29 will cause the balls to move into the groove, being urged to do so by the force of spring H transmitted through the ball race of flange I58. When this occurs, the balls will no longer hold the flanges apart and spring III} will move apart I 58 to the right until the flanges abut, the parts arriving in the positions shown in Fig. 4. In this operation the length of the compression spring Ilii is increased and its effect vis-a-vis the centrifugally-operated parts I92 will be changed and a condition of equilibrium between them can therefore only be achieved under conditions (e. g. at a different speed) different from those which obtained while the balls were out of the groove I83. fhe pitchvarying system will therefore act to maintain a constant speed at a new level which will be determined by the distance of the forward edge of the groove from the position occupied by the balls when governing at the lower constant speed range.

For each range of forward speeds of the aircraft there will be an optimum rotary speed of the propeller which may be pre-selected by varying the spring tension by the means described,

self to changes in forward speed and thereby moves the tube I29 There may, of course, be more than the two pre-selected spring tensions described. The position and extent of each governor setting will be determined by the requirements of each aircraft installation. For example, the propeller system of an airplane having a maximum speed of 260 M. P. H. might be provided with a tube I2ii such as is disclosed in Fig. 7. This sleeve is designed to cause governing to 2109 R. P. M. (maximum engine rated power) from the propeller pitch condition corresponding to G M. P. H. to 100 M. P. H., to cause governing to 1806 R. P. M. (cruising power) from the propeller pitch corresponding to 100 M. P. H. to 1'75, M. P. and to cause governing to 2100 R. P. M. from the propeller pitch corresponding to 175 to 260 M. P. H. (high speed).

The effect of the described apparatus is illustrated by the dotted line in Fig. 6. As the force exerted by spring I I G is decreased when the balls move into the groove, the pitch-changing means .(cylinder 25) must move farther in a pitch-in- :creaslng direction than before in order to overcome the action of centrifugal force on the valve means, and the weaker condition of the spring causes the centrifugally-operated means to overcome its resistance before such occurence while the balls are not in the groove. 4

It is believed that the operation of the invention will be more clearly understood by a consideration of the condition of the various parts at various flying conditions, as shown in the following table:

(1) Aircraft on ground, no forward movement.

. Centrifugal devices as in Fig. 1.

. Spring holds valve as in Fig. l.

. Pressure fluid flows to rear of piston.

. Cylinder at rear limit of movement.

Pitch at minimum.

(2) Takeoff. All conditions same as when aircraft is on ground.

(3) Level flight at first controlled speed.

s ame-e (4) Speed of aircraft continues to increase.

a. Centrifugal devices overcome spring.

b. Valve means moved by centtrifugal means to position shown in Fig. 3.

0. Cylinder moves forwardly to increase pitch, this results in reduction of speed, causing spring to overcome centrifugal devices and move valve to decrease pitch thus increasing speed, etc. etc., until condition of equilibrium is reached.

(5) Level flight at second controlled speed. This occurs when pitch has increased to an amount corresponding to a predetermined forward speed and groove I86 has come opposite balls I 58 causing the spring load to change to the second governing load.

All conditions same as level flight at first controlled speed.

While I have described and illustrated one form which my invention may take it will be apparent to those skilled in the art that other embodiments, as well as modifications of that disclosed, may be made without departing in any way from the scope of the invention, for the limits of which reference must be made to the appended claims.

I claim:

1. A variable pitch propeller comprising a hub, blades journaled in the hub for pitch-changing movement about their respective axes, fluid pres-v sure operated means connected to the blades and movable in either of two directions to effect pitchincreasing or pitch-decreasing movement thereof, a two-part bearing carried by said fluid pressure operated means, means for holding the two parts of the bearing apart, valve means movable to either of two positions to cause pitch-increasing or pitch-decreasing movement of the fluid pressure operated means and to a third position to prevent movement of the fluid pressure operated means, means responsive to the speed of rotation of the hub 'and operable by increases in the speed of rotation to move the valve means to cause pitch-increasing movement of the fluid pressure operated means, a, compression spring eari stone ndl nt hee e veimsa ands enm nnqsi ie ncremention he ame n eusedbrl he spe dzr smn ivemeen en, a d n y creases insneed an e rin at s, e4. 1 d e eaint 0P9 1 1 00? 1,.. PEDart 'h fifl iln mean O erat d r. m redetermine end pi Pit hnc ea in QQVQZWQ 3 9 fluid PF F ne a .m eSiQ 1 a I; emai s d g aid wo: a ts a art to th r by heese e c sth. i 3 h? e inaancl thei q ii y xfi l ii, eby.

'2: T rieble itQ P nelk e r s al bsr lades-iournale r n he ,huh q i har ene mov ment bout $11 t efill l i ra/ 5? uid 1 1%; weropemiedimeansconeeet ta t ed nd m vable n i hetpfi tdire h nc ea ing-.9 i hrdeerea in .l a two-part bearing carried byqs d fluid pressure operated means, valve means' movable to either of two. positions to cause, pitch-increasing, or pitohedecreasing. movement :of ,the ,fluid pressure operated means and .to..a third :position i. to, prevent movement. of V the..fluid pressure operated means, means responsiveeto the speed of rotation of the hub and .operablebyincreases in theispeed of. rotation. to. i move the .valve, means to; .cause pitch-increasing movement of the fluid pressure operated means, a compression spring bearing at one end on the valve means and constantly opposing movement of the valve means caused by the speed-responsive means when acted on by increases in speed and bearing at its other end against one part of said two-part bearing, a plurality of balls between the two parts of the bearing, a cylindrical member carried by the fluid pressure operated means and having an inner surface surrounding the two-part bearing and normally holding the balls between said two parts against the force of said compression spring, said inner surface having an annular groove therein into which said balls escape when the groove is aligned with the balls to thereby cause the two parts of the bearing to be brought together to thereby increase the length of the spring and reduce the force exerted thereby.

3. A variable pitch propeller mechanism comprising a hub, blades journaled in the hub for pitch-changing movement about their respective axes, means connected to the blades and movable in either of two directions to increase or decrease the pitch of the blades, means responsive to the speed of rotation of the propeller for controlling the operation of the blade-moving means, means exerting a force on said controlling means in opposition to that exerted thereon by increases in the speed of rotation of the speed-responsive means and the force of which is constant over a predetermined range of pitch variation whereby the opposing forces of said means maintain a predetermined pitch and constant speed of rotation, and means including a part which is connected to the blade-moving means and is movable therewith, said means being operable upon movement of said blade-moving means in changing the pitch of the blades to an angle outside of such range to change the force of said opposing means whereby the opposing forces of said means maintain a predetermined speed of rotation different from the first.

4. A variable pitch propeller comprising a hub, blades journaled in the hub for pitch-changing movement about their respective axes, fluid pressure operated means connected to the blades and movable in either of two directions to effect pitchincreasing or pitch-decreasing movement thereof,

tain a predetermined constant speed of rotation, and means including apart which-is connected in b as =m v em wsan i q alil ths ewith, said means being ope'rablempon movelnerit;v of said blade rngving means 'in changing the pitch of the blades to" an angle outside of said predetermined range to chan ethe force of said ring means twherebyithe pposineiforc sio f. thee peedrresponsive means and thesnri g means a11 bala cedeat a second. .lev lz o, mainta aipredes termined speed of rotation different from the first.

5. A constant speed variable pitch propeller mechanism comprising a hub, blades Journaled in the hub for pitch-changing movement about their respective axes, means connected to the blades and movable in either of two directions to efi'ect pitch-increasing or pitch-decreasing movement thereof, means operable in response to the opposing forces of opposing means having an equilibruim point to cause pitch-increasing or pitchdecreasing movement of the blade-moving means as one or the other force exceeds the other, means operable during a predetermined range of pitch variation to maintain constant the force of one of said means whereby the opposing forces of said means are balanced at one level to maintain a predetermined constant speed of rotation, and means operable upon pitch change to successive ranges 01' values outside said first range to progressively change the force of said one means to successive predetermined values for each of said successive ranges whereby the opposing forces of said means are balanced at a series of levels to maintain a series of predetermined speeds of rotation each dinerent irom the others.

6. A variable pitch propeller mechanism comprising a hub, blades ournaled in the hub for pitch-changing movement about their respective axes, nuid pressure operated means connected to the blades and movable in either of two directions to eii'ect pitch-increasing or pitch-decreasing movement thereof, a two-part bearing carried by a fixed part of said mechanism, valve means movable to either of two positions to cause pitch-increasing or pitch-decreasing movement of the fluid pressure operated means and to a third position to prevent movement of the fluid pressure operated means, means responsive to the speed of rotation of the hub and operable by increases in the speed of rotation to move the valve means to cause pitch-increasing movement of the fluid pressure operated means, a compression spring bearing at one end on the valve means and constantly opposing movement of the valve means caused by the speed-responsive means when acted on by increases in speed and bearing 75 at its other end against one part of said two-part 1.1., bearing, a plurality of balls between the two parts of the bearing, a cylindrical member carried by the fluid pressure operated means and having an inner surface surrounding the two-part bearing and normally holding the balls between said two parts against the force of said compression spring, said inner surface having a plurality of axially spaced annular. grooves of different diameters therein into any one of which said balls are released when the groove is aligned with the balls to-thereby cause the two parts of the bearing to be brought together by an amount determined by the depth of the groove and the extent of release Of the balls, to thereby increase the length of the spring and reduce the force exerted thereby.

WILLIAM L. GREENE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Name Date 1 Mader June 25, 1940 Dicks Jan. 21, 1941 Caldwell et a1 June 3, 1941 Drake et al Aug. 19, 1941 Englesson Sept. 16, 1941 Warner Dec, 30, 1941 Martin et a1. Sept. 22, 1942 Blanchard et a1. Jan. 5, 1943 Blanchard et al Jan. 5, 1943 Reissner Aug. 10, 1943 Keller Mar. 7, 1944 Lilley Apr. 18, 1944 Hoover Apr. 18, 1944 Richmond July 4, 1944 Whitehead Dec. 5, 1944 French Apr. 24, 1945 FOREIGN PATENTS Country Date Great Britain Aug. 14, 1934 Great Britain Feb. 25, 1938 Great Britain Feb. 20, 1939 Great Britain Feb. 20, 1939 Great Britain Jan. 18, 1940 Germany Feb. 6, 1941 

